Boats in a size range including those used in lobster and crab fishing, usually have a leakage problem where the propeller shaft extends through the hull.
The problem stems from the fact that seals and bearings are attached directly to the hulls thus limiting the types of seals and bearings which can be used and making their servicing, including bearing lubrication, difficult.
Another concern with marine drives is that of enabling thrusts to be accommodated. In that connection, reference is made to U.S. Pat. No. 2,521,368 describing a thrust bearing assembly to be incorporated between the inboard end of the propeller shaft and a universal joint adjacent the engine. The assembly has a housing, held against turning and sealed to the shaft and the universal joint, within which a stub shaft, connecting the propeller shaft and the universal joint, is supported by bearings accommodative of forward and rearward thrusts. In addition, provision was made for introducing a lubricant under pressure into the housing to lubricate the bearings.